The Repository Center and the Pathology Panel for Lymphoma Clinical Studies are headed by pathologists who have specialized in the diagnosis and study of neoplastic diseases of the lymphoid system and are making a joint effort to improve and refine the criteria for diagnosis and classification of these neoplastic diseases, thus assuring the validity of the therapeutic results obtained by their clinical colleagues engaged in therapeutic clinical studies. The Pathology Panel and the Repository Center for Lymphoma Clinical Studies have five major objectives which are closely interrelated: (1) Maintenance of a Pathology Repository Center and Regional Centers for lymphoma clinical studies conducted by NIH supported cooperative groups and of a pathology reference file for clinical study of Hodgkin's disease; (2) Testing the Reproducibility and clinical relevance of the New Working Formulation of non-Hodgkin's lymphoma for clinical usage recommended by an expert international panel; (3) Education of pathologists who are responsible for entry diagnoses of the cooperative protocol studies in an effort to increase the quality of their diagnoses and thereby minimize entry of any patients into protocols to which they do not belong; (4) Furnishing research support for clinical cooperative groups engaged in lymphoma clinical studies; (5) Utilizing the histopathologic material stored in the Repository Center for collaborative research projects closely related to the primary aim. In addition, the Pathology Panel is seeking to incorporate other ancillary methods into a multidisciplinary approach for the diagnosis and classification of malignant lymphomas.